Generally speaking, the basic steps in the processing of color photosensitive materials are the color developing step and the desilvering step. In the color developing step, the exposed silver halide is reduced by the color developing agent to produce silver, and the oxidized color developing agent reacts with a coupler to give a color image. The silver formed is oxidized by means of a bleaching agent in the following desilvering step, and subjected to the action of a fixing agent, thereby converting it to a soluble silver complex, which is then dissolved away, so that only the color image is produced in the color photosensitive material.
In addition to the above basic steps, actual processing will also include various auxiliary steps for maintaining the photographic or physical quality of the image, or for improving image stability, etc. For example, there will be employed a hardening bath, stopping bath, image stabilizing bath and washing bath, etc.
Recently, there has been a considerable demand in the industry for more rapid processing, that is to say, a reduction in the time required for processing. In particular, shortening the desilvering step which takes up nearly half of the processing time has become an important problem.
In general, red prussiate of potash, bichromates, ferric chloride, ferric complex salts of aminopolycarboxylic acids, and persulfates, etc., are known as bleaching agents.
However, because of the problems of pollution associated with cyanide compounds and hexavalent chromium, the use of red prussiate of potash and bichromates requires special processing equipment. Further, in the case of ferric chloride, there are difficulties such as the formation of iron hydroxide in the subsequent washing step and the occurrence of stains, so there are various impediments to its practical application. The bleaching action of persulfates is extremely weak and they have the disadvantage of requiring very long bleaching times. Moreover, there are controls on persulfates as a hazardous material under the Fire Laws, and various measures are required for their storage, etc., so that in general they have the disadvantage of being difficult to employ practically.
Ferric complex salts of aminopolycarboxylic acids (in particular, the ferric complex salt of ethylenediaminetetraacetic acid) are currently the most widely used bleaching agents because there is little problem in terms of pollution therewith and there are no storage problems of the kind associated with persulfates. However, it is difficult to say that the bleaching strength of such ferric complex salts of aminopolycarboxylic acids is wholly sufficient.
As a means for making the desilvering step more rapid, a bleach-fixing solution is known which contains, in one solution, a ferric complex salt of an aminopolycarboxylic acid and a thiosulfate, as described in German Pat. No. 866,605. However, in this case, there is the disadvantage that since the ferric complex salt of the aminopolycarboxylic acid, which inherently has a weak oxidizing strength (bleaching power), is present along with a thiosulfate, which has a reducing capacity, its bleaching power is markedly lowered, particularly, in high sensitive and high silver content photographic color photosensitive materials, it is extremely difficult to achieve sufficient desilvering, and so it is impractical. On the other hand, methods for raising the bleaching power adding various types of bleaching accelerators to the bleaching bath or bleach-fixing bath, or alternatively to the bath before these have been proposed. Examples of such bleaching accelerators are various mercapto compounds as described in U.S. Pat. No. 3,893,858, British Pat. No. 1,138,842 and JP-A-53-141623 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"), compounds which contain a disulfide bond as described in JP-A-53-95630, thiazolidine derivatives as described in JP-B-53-9854 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), isothiourea derivatives as described in JP-A-53-94927, thiourea derivatives as described in JP-B-45-8506 and JP-B-49-26586, thioamide compounds as described in JP-A-49-42349, dithiocarbamates as described in JP-A-55-26506, and arylenediamine compounds as described in U.S. Pat. No. 4,552,834.
Among these bleaching accelerators, there are some which do exhibit a definite bleach accelerating effect, but they are expensive or they have inadequate stability in a bath with a bleaching capability, and so they remain unsatisfactory for a practical use.
In Research Disclosure, RD No. 24023 (Apr., 1984) and JP-A-60-230653, treatment methods are described in which two or more types of ferric complex salts of aminopolycarboxylic acids are used together, but these methods too do not exhibit a sufficient bleach accelerating effect.
Again in U.S. Pat. No. 4,294,914, JP-A-49-84652, JP-A-60-230653, JP-A-62-71954 and JP-A-62-85248, methods are described in which the iminodiacetic acid ferric complex salt, methyliminodiacetic acid ferric complex salt, and hydroxyethyliminodiacetic acid ferric complex salt are used.
However, while there is sufficient bleaching action in the case of the iminodiacetic acid ferric complex salt and the methyliminodiacetic acid ferric complex salt, they have inadequate stability in the bleach-fixing bath, and there is also a problem of stain formation (bleach fogging), etc., so that there are various impediments to their practical use. The bleaching action of the hydroxyethyliminodiacetic acid ferric complex salt is insufficient, and so inadequate for practical use.